ui: add PermissionViewModel with three-state machine

app/src/main/java/de/jeanlucmakiola/calendula/ui/permission/PermissionUiState.kt

@@ -0,0 +1,7 @@
+package de.jeanlucmakiola.calendula.ui.permission
+
+sealed interface PermissionUiState {
+    data object Rationale : PermissionUiState
+    data object Denied : PermissionUiState
+    data object Granted : PermissionUiState
+}

app/src/main/java/de/jeanlucmakiola/calendula/ui/permission/PermissionViewModel.kt

@@ -0,0 +1,27 @@
+package de.jeanlucmakiola.calendula.ui.permission
+
+import androidx.lifecycle.ViewModel
+import dagger.hilt.android.lifecycle.HiltViewModel
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import javax.inject.Inject
+
+@HiltViewModel
+class PermissionViewModel @Inject constructor() : ViewModel() {
+
+    private val _state = MutableStateFlow<PermissionUiState>(PermissionUiState.Rationale)
+    val state: StateFlow<PermissionUiState> = _state.asStateFlow()
+
+    fun onGranted() {
+        _state.value = PermissionUiState.Granted
+    }
+
+    fun onDenied() {
+        _state.value = PermissionUiState.Denied
+    }
+
+    fun onRetry() {
+        _state.value = PermissionUiState.Rationale
+    }
+}